Remote controls are used to control the operation of various consumer electronics, such as a television (TV), a video cassette recorder (VCR), and a digital video disk (DVD). Many such remote controls transmit an infrared signal that is obtained by pulse period modulation (PPM) or alternatively known as space width modulation (SWM) or variable space modulation (VSM) of a carrier wave (e.g. oscillating at 38 kHz). As illustrated in FIG. 1A, a bit of value zero (0) is indicated in the signal by a pulse 1 of the carrier for a duration H0 followed by a low period of duration L0, for total length of 1.12 milliseconds. Similarly, a bit of value one (1) is also indicated by a pulse 2 of the carrier for a duration H1 followed by a low period of duration L1, for total length of 2.24 milliseconds. The pulse duration is normally the same, e.g. H0=H1 regardless of the bit's value being zero or one. As illustrated in FIG. 1A, the only difference between representation of these two bits is the duration of the low periods L0 and L1 (wherein L1>L0).
Each touch of a button on the remote control results in transmission of a header 3 (FIG. 1B) which lasts 9 milliseconds, followed by a quiet period of 4.5 milliseconds, followed by a variable length data transmission (labeled as bits A0–A15 in FIG. 1B) lasting 45 milliseconds to 63 milliseconds that identifies the remote control (also called “remote control identifier”). Bits A0–A15 are followed by another variable length data transmission (of similar duration) that identifies a button that was pressed on the remote control (also called “button identifier”). The button identifier normally includes two portions: an 8 bit key code (labeled D0–D7 in FIG. 1B) followed by an inverse of the 8 bit key code (labeled ˜D0–D7 in FIG. 1B). For example, if the key code that was encoded in bits D0–D7 was of value “A1” (in hexadecimal), then the value “5E” which is the inverse of value “A1” is transmitted immediately thereafter. In this example, the button identifier is transmitted as “A15E.”
Computers of the prior art may have a built-in port in conformance with the IrDA standard which is described in, for example, the following documents, each of which is incorporated by reference herein in its entirety: serialinterface.pdf, PointandShootvlp1.pdf, and IrDA_Dongle_Vlp2.pdf, from the Infrared Data Association (SM) (from www.irda.org).
When a remote control is operated in the vicinity of a computer's IrDA port, a photodiode in the port may sense the signal emitted by the remote control. However, the remote control signal is not decoded correctly by the IrDA port for a number of reasons, e.g. due to difference in modulation schemes, difference in baud rate, and difference in byte encoding (e.g. presence/absence of start bit, stop bit and parity bit). Therefore, the IrDA port normally rejects a remote control signal, for not conforming to the IrDA format. Such rejection ensures that communication between two IrDA compliant devices is not disturbed by stray noise from remote controls and other devices.
It is known in the prior art to custom build circuitry 5 in a computer to receive signals generated by a remote control as described in the following documents, each of which is incorporated by reference herein in its entirety: remote.html and ir_experience.html (from www.armory.com).
However, such custom circuitry is relatively expensive to build, cumbersome and not easily available to the average user. Therefore computers currently are not normally operated by a remote control, as easily as consumer electronics.